The present invention relates to blood drawing devices, and more particularly a blood drawing device that has a needle, or cannula, internally coated with an anticoagulant so that when the needle is used to puncture the artery or vein of a patient, blood that flows through the needle is clot free.
In the medical field, in addition to being known as one of the more important medications, heparin is used to inhibit coagulation of blood drawn for blood gas analysis and other laboratory tests. In conventional commercial blood drawing tubes or syringes, the final concentration of heparin is known to be about 3-200 units/ml. This concentration of heparin is by far and away sufficient to anticoagulate blood drawn from a patient.
Based on a study carried out by the departments of pathology, biochemistry and pediatrics of the University of Colorado Health Sciences Center in Denver, Colo. the concentration of heparin (bovine sodium heparin) necessary to inhibit clotting was found to be 0.6 and 0.75 units/ml of plasma and 0.4 and 0.6 units/ml of whole blood. No visual clots or instrumentation interference due to micro-clots were observed in whole blood anticoagulated with a minimum of 1.0 unit/ml of heparin after 20 minutes at room temperature or 75 minutes at 4xc2x0 C. At 4xc2x0 C., the minimum heparin concentration to inhibit whole blood from clotting for over 4 hours was 0.75 unit/ml.
However, since most manufacturers of blood drawing devices use some form of dry heparin (vaporized or lyophilized) in the body of the device, occasional premature clots particularly inside the inner surface of the cannula would occur. So, too, because of the different degrees of roughness of the inner surface of the cannula and the uniqueness of the clotting factors which vary from individual to individual, it is not uncommon for micro-clots to form in the blood prior to the blood reaching the bulk of the heparin in the blood storage device This phenomenon does not occur in blood drawing devices that contain a form of liquid heparin. This is due to the fact that as the excess liquid heparin is expelled prior to use (by the user pushing the plunger of the syringe in the direction of the needle), the inner surface of the cannula is indirectly coated, thereby enabling the blood to be in contact with the anticoagulant as soon as it is drawn from the patient. But, a problem does arise with the use of such blood drawing device because of the dilution effect that liquid heparin has on the blood drawn, as the accuracy of the measurement of the various components in the blood drawn from the patient is affected by the blood having been diluted with the liquid heparin.
In view of the disadvantages of the conventional types of blood drawing devices coated with dry heparin and liquid heparin, there is therefore a need for a blood drawing device coated with an anticoagulant that will not cause micro-clots or be affected by any dilution effect of the blood withdrawn from the patient. Putting it differently, there is a need for a blood drawing device that would not adversely influence the analysis of pH/blood gases co-oximetry, electrolytes and metabolites of drawn blood.
To overcome the disadvantages of the prior art blood drawing devices, the present invention blood drawing device has the interior or inner surface of its needle, or cannula, atomized with a liquid anticoagulant by an ultrasonic atomization process. The thus atomized cannula is then dried, either by air or by heat so that the interior surface thereof is coated with a layer of anticoagulant at a concentration that comports with the above-noted study done by the University of Colorado Health Sciences Center. The thus anticoagulated cannula of the present invention can be used with a syringe, or container, that is fitted with an air bubble removable filter such as the FILTER-PRO(trademark) of the assignee, The syringe can also have attached thereto the needle protection sheath (NEEDLE-PRO(trademark)) of the assignee.
An objective of the present invention blood drawing device is to prevent any clotting effect that may occur when a cannula is used with a blood withdrawing device.
Another objective of the present invention is to provide a blood drawing device having a cannula that does not require to be coated by any liquid heparin just prior to its being used.
Yet another objective of the present invention is the provision of a blood drawing device that has a stable, non-reactive coating of an anticoagulant already formed in the inner surface of its cannula, so that the device has an extended period of shelf store life and can be used right from the package.